There is nothing abnormal with your CV. It just shows there is no reduction within the potential window you are scanning. The oxidation you observe is probably related to the solvent. Possibly you are using a graphite/carbon electrode, and the electrode is not oxidized. If on the other hand a for example gold electrode was used then a well defined reduction peak would be observed at +/- 0.8V (depending on pH). However if you scan further in the negative direction (say to -1.5) you will observe reductive current. Assuming the solvent is water, the reduction potential will also be dependent on pH.

Best regards, Mike

I am using Carbon nanotube paper(CNP) as a counter electrode and Nickel cobalt sulfide/CNT is my working electrode in 6M KOH electrolyte. Last but not the least, thank you sir for your nice comments

The air-cathode phototrophic MFC, however, had no Biofilm formed on the cathode and did not show a negative current under the light (Figure S1), suggesting that the cathodic Biofilm of the sediment phototrophic MFC played a role in the reversed current generation. In addition to oxygen effect, substrate changes may also contribute to current reversal (30), though the exact reason remains unclear.

The negative effect of oxygen can be alleviated by using color filters to filtrate the full-spectrum light or increasing the thickness of the sediment layer on the anode. Color filters would not completely inhibit the activities of photosynthetic microorganisms because most of them have a wide adsorption spectrum (31). Instead, color filters may lessen oxygen evolvement by reducing light strength. However, it requires further investigation on how the photosynthetic microorganisms in this study were affected by red or blue light.

Zhen He et al., 2009 : Self-Sustained Phototrophic Microbial Fuel Cells Based on the Synergistic Cooperation between Photosynthetic Microorganisms and Heterotrophic Bacteria. Environ. Sci. Technol., 2009, 43 (5), 1648-1654• DOI: 10.1021/es803084a • Publication Date (Web): 02 February 2009

Downloaded from http://pubs.acs.org on April 12, 2009

In that case there might be a problem with the preparation of the Ni-Co-S electrode, which should show vigorous activity between 0 and 0.5 V vs. Ag/AgCl. From your CV it seems there is no electric contact between the Ni-Co-S and CNT, this could be related to many things (to much binder, incomplete evaporation of additives etc...), all depending on the method of synthesis/modification. Which of course is not always straightforward.

Good luck, Mike

yes it is necessary to scan towards the negative side, might observe the negative peak (reduction current).

It is depende to your electrodes material behavior